Ulcerative colitis (UC) is a chronic, inflammatory disease of the colon and rectum. It’s one of two main inflammatory bowel diseases, the other being Crohn’s disease.

When a person has UC, sores called ulcers develop inside the colon.

Symptoms of the disease include:

Researchers don’t know for sure what causes UC, but they think it may be caused by a misdirected immune reaction. Numerous things may trigger a flare, including certain foods.

Much is being learned about the role of diet and gut bacteria in inflammatory bowel diseases, but some research is still in its infancy.

However, the Academy of Nutrition and Dietetics, the World Gastroenterology Organization, and the Crohn's and Colitis Foundation of America all agree that fiber is a protective nutrient for the colon.

Fiber should only be reduced when you are experiencing acute symptoms like a flare-up or strictures.

During a flare-up of symptoms, a low-fiber diet may be helpful in reducing material in the colon, and thereby reducing symptoms and helping you recover more quickly.

If your doctor has prescribed a low-fiber diet for your symptoms, follow the recommendations below. Otherwise, follow a high-fiber diet.

Foods that contain a lot of fiber tend to be difficult for people with UC during a flare-up to digest. Whole grain flour is high in fiber because it hasn’t had the germ or bran removed.

You should avoid eating food made from any whole grain flour, such as:

  • breads
  • cereals
  • pastas
  • noodles
  • macaroni

During flare-ups, choose white breads and pastas made from enriched white flour, unless you have a gluten intolerance.

Flour is “enriched” when nutrients lost during the germ and bran removal process are replaced. Cereals like puffed rice, corn flakes, and cream of wheat are also lower in fiber.

Avoid the following whole grain foods:

  • brown rice
  • quinoa
  • buckwheat
  • oats
  • wild rice

These grains still have the fibrous endosperm, germ, and bran that can irritate UC and may trigger a flare-up.

Avoid these other whole grains:

  • plain barley
  • millet
  • wheat-berries
  • bulgur wheat
  • spelt

A better option for those with UC is well-cooked white rice.

Nuts, including those cooked into other foods or made into flours, should be on your do-not-eat list if you have been prescribed a low-fiber diet for UC. The fiber in nuts can be very hard to digest.

It’s best to avoid the following nuts:

  • walnuts
  • hazelnuts
  • pecans
  • cashews
  • almonds
  • macadamia nuts
  • peanuts
  • pistachios

Like nuts, seeds can also aggravate symptoms. Seeds are a type of insoluble fiber, which can cause bloating, diarrhea, gas, and other irritating side effects.

Some seeds to avoid include:

  • sesame seeds
  • flax seeds
  • millet
  • pine nuts
  • sunflower seeds
  • pumpkin seeds
  • wild rice

Legumes, including beans, lentils, and peas, are high-fiber, high-protein foods. Because of the indigestible sugars in beans, they’re also notorious for causing gas. If you are experiencing a UC flare-up, you’ll want to pass on the following:

  • all beans, including chickpeas
  • adzuki beans
  • soy nuts, including soybeans and edamame

While they are healthy for you, most fruits contain a lot of fiber. Fruits belong on the list of foods to avoid if they are:

  • raw
  • dried
  • have seeds that can’t be removed (like most berries)

You can eat fruit that’s been peeled and if the flesh has been cooked until very soft, such as applesauce. You can also eat canned fruits, but choose the type packed in water or in their own juice to avoid excess sugar.

Most fruit juices are fine to drink, but only with the pulp removed. Skip prune juice since it’s very high in fiber.

Like fruits, vegetables are also full of fiber. Include them in your diet only if they are:

  • skinned or peeled
  • have no seeds
  • are cooked until soft

Avoid all raw or undercooked vegetables, including corn. It’s fine to consume canned vegetables and potatoes, as long as the skin has been discarded. Try pureed vegetable soups for an easy way to digest vegetables.

Vegetables provide many important nutrients and it’s important to incorporate them in your diet.

Sulfate is a required nutrient in the human diet that assists in many body processes, however, it can also feed certain bacteria that create H2S toxic gas in the a person with UC. In fact, over 90 percent of people with UC make H2S gas rather than the normal methane gas.

If you find yourself experiencing bloating and malodorous gas, you may have an overabundance of these types of bacteria in your colon, excess sulfate and sulfides in your diet, or both.

Sulfate and sulfide rich foods to reduce include red meat, dairy milk, beer and wine, apple and grape juice, cruciferous vegetables, eggs, cheese, dried fruit, and some well water.

A common food intolerance among those with UC is dairy. If you suspect dairy may be a symptom trigger for you, remove all types of dairy including butter, milk, yogurt, and cheese for at least four weeks.

Work closely with your doctor or dietitian to help you learn how to follow an elimination diet.

A food intolerance that is becoming more common among those who have digestive symptoms is gluten.

Gluten is one protein found in wheat, rye, and barley. Gluten is not only found in common foods like bread and pasta, but is also added to prepared products like condiments, sauces, soups, and proteins.

If you suspect gluten may be a symptom trigger for you, remove all types of gluten-containing grains, cereals, baked goods, and other products for at least four weeks.

While your diet may be restricted if you are experiencing a UC flare-up, it doesn’t have to be boring. Focus on the foods you can eat rather than the foods you should avoid. The foods you can eat (unless you have an identified allergy or intolerance to any of the foods below) include:

  • white bread without seeds
  • white pasta, noodles, and macaroni
  • white rice
  • crackers and cereals made with refined white flour
  • canned, cooked fruits
  • cooked vegetables without skins or seeds
  • pureed vegetable soups
  • tender, soft meats (no gristle or skin), and fish
  • peanut butter and other nut butters
  • oils like olive oil and coconut oil

It’s important to remember that your diet plays a vital role in your overall health. Use this information as a guide to help you recover from acute symptoms like diarrhea, strictures, or after surgery.

To increase your chances of remission, gradually reintroduce high-fiber foods, since fiber protects the health of your colon tissue as well as your gut bacteria.